<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>组合选择器</title>
    <style>
        /*后代选择器*/
        .center li {
            color: blue;
        }

        /*分组选择器*/
        span,p{
            color: red;
        }
    </style>
</head>
<body>
<div class="top">
    <ol>
        <li>aa</li>
        <li>bb</li>
    </ol>
</div>

<div class="center">
    <ol>
        <li>cc</li>
        <li>dd</li>
    </ol>
</div>

<span>span</span><br>
<p>段落</p>
</body>
</html>